Electron Push-Pull Effect Drives Reversible Six-Electron Redox Reaction in Aqueous Zinc-Dual Halogen Batteries.

Four-electron aqueous zinc-iodine (Zn-I2) batteries with I-/I0/I+ conversion could achieve high energy density, but the development is largely impeded by I+ hydrolysis and sluggish redox kinetics. Here, by introducing 1-ethylpyridine hydrobromide (EB) as an electrolyte additive, we designed aqueous zinc-dual halogen (iodine-bromine) batteries to address these issues, which enable reversible six-electron conversion with high capacity and long-term cycling stability. In situ X-ray absorption spectroscopy, Raman spectroscopy, and theoretical calculations reveal that the donor-acceptor interactions within I-Br interhalogen compounds induce an electron push-pull effect, enabling a kinetically enhanced four-electron pathway (I-/I2Br-/IBr2-) followed by an activated two-electron pathway of bromine (IBr2-/IBr3-) upon charging, while partial IBr3- undergoes an I+/Br0 co-reduction reaction with enhanced bromine utilization during discharge, leading to asymmetric yet overall reversible six-electron conversion. In addition, the cation groups of EB reconstruct the H-bond network of bulk water and electrostatically anchor IBr2- and IBr3- species, thereby reducing the water activity and stabilizing the interhalogen compounds. These synergistic effects enable zinc-dual halogen batteries to achieve a remarkable capacity of 656 mAh g-1 at 0.5 A g-1 and sustained cycling stability with a high initial capacity of 436.8 mAh g-1 over 2200 cycles at 10 A g-1. This work extends the application of interhalogen chemistry for constructing high-energy-density aqueous batteries with multielectron redox reactions.